1. Field of the Invention
This invention relates generally to a method and apparatus for forming a cooling interface for an electronics package mounted to a cooling assembly and more particularly to a method and apparatus for heating a thermstrate element in the cooling interface of a high power RF microwave transmit/receive module during replacement in an active aperture of a radar system.
2. Description of Related Art
In a typical active aperture for a pulsed radar system, a large number of replaceable plug-in type high power transmit/receive (T/R) modules are arranged in a predetermined configuration and connected to an array of forwardly located radiator elements which collectively transmit and receive a beam of RF pulses to and form a target. Such a system is shown, for example, in U.S. Pat. No. 6,005,531, entitled xe2x80x9cAntenna Assembly Including Dual Channel Microwave Transmit/Receive Modulesxe2x80x9d, issued to John W. Cassen et al. on Dec. 21, 1999. The transmit/receive modules themselves are further shown and described in U.S. Pat. No. 6,1141,986, entitled xe2x80x9cDual Channel Microwave Transmit/Receive Module For An Active Aperture Of A Radar Systemxe2x80x9d, issued to John W. Cassen et al. on Sep. 5, 2000.
These high power T/ R modules, however, must be cooled efficiently to optimize overall transmit/receive module reliability. The method of providing an efficient thermal interface in the system of U.S. Pat. No. 6,005,531 is achieved by means of a thermstrate preform and miniature wedge lock assembly which holds the module tightly against an assembly including an elongated liquid coolant circulating coldplate connected to a coolant distribution manifold.
The medium used to fabricate a thermstrate is comprised of a paraffin-like coating typically 0.001 inches thick, applied to both sides of a 0.002 inch thick aluminum carrier. The function of the thermstrate is to fill surface imperfections and air gaps of the thermal interface, thereby increasing the cross section of thermal conduction path. To fill these voids, the wax must be liquefied or xe2x80x9creflowedxe2x80x9d. Liquefying the wax is a simple matter of heating the joint to the melting point of the wax while maintaining enough pressure to keep the wax in that joint. Once cured with the removal of heat, the resin is a thin, slightly bonded joint with a very low and attractive thermal impedance, on the order of 0.04xc2x0 C. in2/W.
The use of a thermstrate preform, however, presents a problem when a T/ R module requires replacement. A typical antenna assembly such as shown in U.S. Pat. No. 6,005,531 is comprised of several hundred T/R modules. During assembly, a pre-cut thermstrate preform is tacked onto the external bottom surface of the modules"" heat sink, whereupon they are installed into the array assembly while mating with assigned RF connectors. Once all of the required modules are in place, small wedgelocks are installed. These wedgelocks when torqued, clamp each T/R module to a liquid filled coldplate assembly. The preinstalled thermstrate is therefore clamped between the T/R module and its coldplate. The assembly is next subjected to a thermstrate reflow process which can be achieved, for example, by placing the entire antenna in an oven or heat the coolant fluid flowing in the coldplate to a specified value so as to melt the thermstrate. The latter method is usually the one preferred.
During normal usage, some of the T/R modules will inevitably fail or perform less than desired, thus requiring replacement. Removing a T/R module is a simple task. For example, wedgelocks are loosened around the module in question and it is pried away. The module is then disengaged from its RF connectors and removed from use.
To prepare the site of the removed module for a replacement T/ R module, the site need only be cleaned of any residual wax buildup. A new module with thermstrate is then installed, engaged into its connectors, and clamped to the coldplate with the wedgelocks. To reflow the thermstrate for a single or handful of replacement modules, the above stated scenario outlined above must be repeated, e.g., heat the coolant fluid for the entire antenna. This task can be a very time consuming, cumbersome effort to reflow a small quantity of modules. It is to this task that the subject invention is directed.
Accordingly, it is an object of the present invention to provide an improvement in the method of replacing a plug-in type T/R module in an antenna assembly.
It is a further object of the invention to provide an improvement in the reflow process of a thermstrate located on the T/R module when a T/R module is set in position against a coldplate.
In one aspect of the invention, it is directed to a method of optimizing the heat conduction path in a thermal interface between an electronics package and a mounting assembly which also provides cooling of the electronics package, comprising the steps of: locating an electrical heating element on or in the electronics package; locating a meltable interface member between the electronics package and the mounting assembly and which has a specified melting point upon the application of a predetermined amount of heat; applying electrical energy to the heating element so as to heat the member to the melting point for a predetermined time, causing material of the member to fill surface imperfections and air gaps in the thermal interface; and, thereafter curing the member by the removal of heat with a resulting interface bond being formed between the electronics package and the mounting assembly.
Another aspect of the invention is directed to apparatus for facilitating the mounting of an electronics package to a mounting assembly which includes a cooling capability and having a thermal interface therebetween including an interface member having a specified melting point which when melted, fills surface imperfections and air gaps between the electronics package and the mounting assembly, comprising: a heating element located in the electronics package for generating heat sufficient to melt said interface member on demand during initial assembly or replacement; and a pair of electrical contacts located on an outer surface of the electronics package for the connection of an external source of electrical energy to said interface member.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific example, while indicating the preferred method and embodiment of the invention, are given by way of illustration only, since various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.